This application is based on an application No. Hei 10-266757 filed in Japan, the entire content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a unit and method for controlling printers connected via a network, a record medium recording a control program, and a printer system.
2. Description of the Related Art
With recent expansion of a networked office environment, an increased number of printers are used in connection to PCs (personal computers) via networks. Likewise, a growing number of digital copiers also used as the printers are connected to PCs via networks. Consequently, mixed networks interconnecting PCs, printers and digital copiers have increased.
Such printers and digital copiers incorporate printer control units. The printer control unit requires more memory to cope with recent progress in digitization, color printing capability and speedup of the printers.
For instance, a printer generally called a page printer requires an image memory for at least one page print job. For more effective presentation of high-speed capability, the printer must have an even larger image memory. Further, an increasing number of printers are capable of printing both sides of sheets for paper saving purposes stemming from the current environmental problems. Such a printer requires a memory twice as large as a printer for one side print has, because the image memory must have capacity for data of a two-page print job. On the other hand, a color printer must have a memory eight times as large as a memory of a monochromatic printer. A color printer of a 257-step gradation requires a memory eight times as large as a memory of a printer of a two-step gradation. In a color printer of 400 dpi and the 256-step gradation, for example, a quantity of image data for an A4 size print is about 60 MB, requiring a memory of a corresponding capacity.
Because of restriction on access speed to the memory, the printer control unit requires a semiconductor memory as a usable memory (an expansion memory for expanded image data) . That is, printer control unit is expensive, including lots of semiconductor memories.
For effective use of the expensive printer control unit, a system has been proposed wherein a single printer control unit is contained in a casing independently from the printer and digital copier rather than incorporated in each printer and digital copier, thereby providing control of plural printers and digital copiers connected via a network.
Unfortunately, the following problem is encountered in the system wherein a single printer control unit controls plural printers.
In a case where the printer control unit has only as much memory as to provide control of one printer, it is impossible to control a plurality of printers at a time. That is, an image memory with the double capacity is required for simultaneous control of two printers. This presents a serious problem in terms of costs.
To solve this problem, it is contemplated to compress image data for image memory saving.
Recently, image data compression techniques have been applied in many fields. For instance, there has been proposed a technique applied to a digital complex system providing operation controls through selective connection of a copier unit, facsimile function unit and the like (Japanese Unexamined Patent Publication No. 5(1993)-75768). In this system, a data compression ratio is selected such that a compression ratio of the facsimile function unit differs from a normal ratio of the copier unit, the facsimile function unit requiring a high speed processing for telephone charge saving.
It is an object of the invention to solve the aforementioned problem.
It is another object of the invention to provide a printer control unit and method which provide simultaneous control of a plurality of printers connected via a network.
It is still another object of the invention to provide a printer control unit and method which provide simultaneous control of a plurality of printers connected via a network without using a large memory.
These and other objects are attained by a printer control unit which comprises an interface for receiving image data from an external source and for transmitting image data to external printers, a memory storing the received image data; and controller for compressing the received image data for transmission to a second printer and storing the compressed image data in the memory when image data in the memory is transmitted to a first printer
The above objects are attained by a printer control unit which comprises an interface for receiving image data from an external source and for transmitting image data to external printers, a memory for storing image data, first controller for compressing the received image data at a first compression ratio and storing the compressed image data in the memory, and second controller for compressing the received image data for transmission to a second printer at a second compression ratio and storing the compressed image data in the memory when image data is being sent from the memory to a first printer.